R.G. Keen has an amp series coming out

[R.G.]

my sympathy for being worked over by such a tuff crowd. I'm sure you are aware that we are not the general guitar amp buying public.

It *is* a tough crowd, but it's the one that matters - people who take their gear and their tone seriously. I have no problem with constructive criticism at all.

I mean this in all seriousness:
All comments, both for and against the cosmetics are welcome. I'm taking notes, although I may not respond to each one individually. The info is getting funneled back to the rest of the cosmetics group. It may change, it may not, but they will be aware.

Some things that the recent comments sparked, that may not show in the artist's drawing:
- there is no grille cloth at this point, the hubcap/jet intake is front mounted.
- the speaker is rear mounted on the baffle.  Speaker mounts  in to Tee-nuts, not screw-in threaded studs, by the way. The baffle board will give way before the speakers will come loose. I believe (although I have not tested!) that an impact sufficient to tear the speakers loose would destroy the speaker and/or rest of the rabbeted-and-glued hardwood plywood box.
The 2-12 version has a stiffener glued into the back of the baffle between the two speakers.
- the baffle board is finished in dull pebble finish, not grille cloth
- the tan/brown front piece is leather colored tolex, not woodgrain.
- the hubcap/intake is about 1.5" thick; the baffle is inset enough to protect the hubcap
- the hubcap is removable from the front, eight screws which are NOT the same screws that hold the speaker on. Although I'm not advocating for or against this, it **could** be easily painted, covered, or otherwise finished to suit an individual owner's taste.

For more of a retro/tekno look, do away with the conventional grill all together. Just put a hole in the front baffle for the speaker (which would be rear mounted) and put the hubcap/diffuser directly to the front of the baffle.

You been snooping in my mechanical drawings???

The baffle would be covered with hot pink snake skin like the rest of the cabinet (just joking).

Our custom shop (that's me...) will be happy to provide a quotation on ...um... highly individualized units. Hot pink snake skin -is- quite expensive, though...  

Quoting my instructor in my first strategic negotiations classes " There's always a number which can make any request work."

Beware though ... UL approval.

Thanks, C.J. I've had to baby sit a couple of approvals, and yes, you want to look the testers in the eye while it's being done. Always good practice.

who cares how it looks, i want to hear how it SOUNDS!

Ah! You, sir, are our target demographic!!

[Hailstorm350]

I think you missed my question, is it A or A/B or R/G  jk :lol: ?
knowing you, you would come up with some special way to implement the power tubes that no one except the military has come up with... pancake switches, who would've thought?



Ken

[object88]

I would guess that at 30 and 60 watts, it's A/B.  You could do 30W at class A, but you'd need a smegload of tubes for 60W of class A.

[Hailstorm350]

thanks object, I kindof thought so, but Pure A does seem to sound better to my ears.

[Regan]

Hi RG.,
Hope I wasn't coming across too critical:)
One somewhat practical suggestion I can make would be corner guards of some sort, they would protect the amp in the long run.
An off the wall idea that might interest you is since it has power for pedals, what about making the cabinet a little taller and have a slide out pedal board so you carry the amp to the gig, slide the pedal board from the bottom of the amp hook up the cables and your done.
I don't know how many times I have seen amps that people have shoved cables and pedals etc into the back of the amp and punctured the speaker etc. I don't think the development or implementation would cost much per amp, and for the investment you would be adding a lot of convenience for the common musician I think.
Regan

[R.G.]

think you missed my question, is it A or A/B or R/G jk

oops... sorry, yes, I did.

It's AB. The 30W is the one that we thought would get lots of air time, so we used 6L6/EL34 in that amp as well. The tubes are NOT being stressed, so they should last a long time.

but Pure A does seem to sound better to my ears.

Yep, mine too. But making it 30W class A would have run the price up. A lot.

Hope I wasn't coming across too critical:)

Not at all. I'm not getting much of a sense of put-down here at all. I believe people are really trying to be helpful.

One somewhat practical suggestion I can make would be corner guards of some sort, they would protect the amp in the long run.

Actually, they have been added since the artist's drawing was done.

An off the wall idea that might interest you is since it has power for pedals, what about making the cabinet a little taller and have a slide out pedal board so you carry the amp to the gig, slide the pedal board from the bottom of the amp hook up the cables and your done.
I don't know how many times I have seen amps that people have shoved cables and pedals etc into the back of the amp and punctured the speaker etc. I don't think the development or implementation would cost much per amp, and for the investment you would be adding a lot of convenience for the common musician I think.

That's a good idea. We talked over several semi-radical ideas for the amp mechanical layout, including an integrated roller-cart something like the air travel bags, and attachments for effects. We finally stopped with the idea that if it sells enough to get back our investment, we can talk more about radical ideas. But I'll put that into the ideas file. Thanks!

[WGTP]

I may have missed it, but what is the hubcap/diffuser/free air impedance matching dispersal unit made off?   :shock:

Funny, I was just thinking about a 2 or 4 12" SEALED cabinet with an extra speaker mounted in back.  That way you keep the lows of a sealed cabinet with the air/ambience/dispersion of an open back cabinet, especially if there is a back wall within several feet.  

[puretube]

welcome to The Club...  

[runmikeyrun]

All good ideas need some controversy to get them some publicity and jump start sales.  It worked for 2 Live Crew and it could work for you too.  the hubcaps are definitely eye catching but your older crowd might dismiss the amp totally regardless of how good it sounds based on them alone.   I'm looking at this amp and seeing a lot of "older" classic rock type guys buying it so you don't want to scare them off with something that looks like a sub box in the back of a 2004 Civic.    What about making them removable?  You might be able to utilize some sort of ball and sockets like the way speaker grilles for home stereos are held on.  You could picture them in the ads with and without the diffusers.  Include them with the amp and let the customer remove them if they are not sold on them.  Just an idea...

otherwise they look like a great amp!  Knowing what you know i'm sure they will sound amazing and be rock solid reliable.  Let us know when we can go down to Guitar Center to play em!

[Fret Wire]

From this new thread:
http://diystompboxes.com/sboxforum/viewtopic.php?t=35520

The phillips screwdriver to the left of the amp is what we came to call the Workhorse Bias Adjustment Kit. The internal bias lights really seem to work well. I'm normally pretty careful about which tube is which, and usually label them so I don't have to rebias. In the preliminary messing around with the amp, I got downright insensitive to which tube was which or even which pair of tubes I was using because rebiasing was a matter of letting it warm up and then diddling the bias pots til I got two green lights. Biasing is a breeze.

This is the "easy user biasing", vs the "auto biasing" on the larger models. Can we get into what the ckt shoots for (green lights) in terms of plate voltage and idle current? Is it even measuring plate voltage and ma? Wouldn't seem like it, too dependant on the tubes themselves, and the adjustable range of safe operation too big.

You can also use a special purpose instrument that nulls the input signal out of the output signal so that you can monitor just the distortion products. You then adjust the bias to get the distortion to a realistic minimum without making it dramatically less than the residual THD. This is the premium method, but requires a distortion analyzer - big bucks.

These methods can be more accurate than the first two methods but they require expertise and tools that most folks don't have.

If you are a circuit hacker, and live on solder fumes and cold coffee, you can modify the amp with solid state servo bias adjusters that twiddle the bias to each output tube on the fly on a continuous, real time basis to keep each tube -* exactly *- where it ought to be. Only recommended for real wiring fanatics...

Along these lines? I guess I'm more curious about what parameters it looks for than how it looks for them. You're not a fan of the cross over method, correct? I always assumed the manufacturer's were using some kind of scope method during R & D. I always do it by ear, paying no mind to the plate voltage and current as long as they are within safe limits.

Was there any particular tube manufacturer's data sheets you referenced when setting this up for the 6L6/EL34's?

[R.G.]

This is the "easy user biasing", vs the "auto biasing" on the larger models. Can we get into what the ckt shoots for (green lights) in terms of plate voltage and idle current? Is it even measuring plate voltage and ma? Wouldn't seem like it, too dependant on the tubes themselves, and the adjustable range of safe operation too big.

It is indeed the "easy user biasing". There's not much magic in there - it reads tube cathode current at zero signal and then puts that into a tight window comparator. When you have a green light and only a green light, the currents are the same within about half a milliamp.

I picked the target currents based on interviews with some amp techs I respect. They all had their own ideas, but they clustered pretty closely when you translated that into cathode current.

It's by no means perfect - but then, given the wide range of tube characteristics and the wide range of acceptable biasing points, it doesn't have to be. This method reads the plate plus screen current. However, I find little to choose between purely plate and plate plus screen currents as a standard for biasing.

I guess I'm more curious about what parameters it looks for than how it looks for them.

It's reading cathode current, pure and simple. In that, it mimics what 99.9% of all amp techs do when they bias an amp.

I know that some people try to bias to a given power level. However, given a (kind of) fixed power supply, power level is linear with biasing current. The cleanness of crossover is more a function of tube current than it is power.

You're not a fan of the cross over method, correct?

Absolutely not; at least to the extent that the "crossover method" puts the signal up on a scope and you then adjust bias until the crossover disappears. You can read more about my ideas of biasing in the Tube Amp FAQ at GEO. It is incredibly difficult to get consistent results by eyeballing crossover on a scope. The only way this ever works is that tubes have such a big "OK" zone for biasing. It's very seductive to bias it just a little hotter each time. Numbers are less subject to seduction, so any method that does not involve a human thinking it's "good enough" works more reliably.

I always assumed the manufacturer's were using some kind of scope method during R & D.

I'm sure some do. But it's not reliable unless the scope is also hooked up to do data reduction for you.

I always do it by ear, paying no mind to the plate voltage and current as long as they are within safe limits.

If it works for you, great. Most people get them too hot this way, but some people can do it.

Was there any particular tube manufacturer's data sheets you referenced when setting this up for the 6L6/EL34's?

I read all of them I could. Today's tubes are all over the map, and I assumed that buyers would use anything. So I tried to put the bias points where it would hit the good zone for a cross section of tubes.

The problems with this approach are also its virtues. It is not all that flexible, in that you only get one smallish region where you get a green light per tube type, and I selected the bias points. If you want green plus 15%, there's no good way to judge that. You can still probe the circuit and set the currents to whatever, ignoring the lights.

There's a good analogy that came up at the show. We're trying to build a hammer. If you have a large number of nails to hammer in, you want a hammer. You don't want a hammer with a corkscrew attachment, a screwdriver attachment, a wrench adapter and so on. You want a hammer. You probably don't want a solid titanium gold plated hammer with a cryogenically stress relieved face unless you're also a world class olympic carpenter. The idea of the Workhorse amps is to make a musician's tool - you go out to a gig, it works; there's a minimum of muss and fuss in using it, and it's easy to repair if it ever does break. It's flexible in making different sounds, but it's probably not the amp for someone who wants to mess about with the innards of an amp a lot - it's for players.

[Fret Wire]

Thanks for the in-depth reply.  Cathode current...ok, I was expecting something unusual (magic), simple is good.

You're right about x-over method, the cross over point disappears, or you think it did, or you think it didn't...you go mad, and end up measuring current and voltage anyway. That's my take the one time I tried it. I always thought somewhere out there, was reliable a scope method only shared by the companies and a few others. Wishfull thinking I guess.

Quote:

I always do it by ear, paying no mind to the plate voltage and current as long as they are within safe limits.  

If it works for you, great. Most people get them too hot this way, but some people can do it.

I put that too simplistically, I do always ckeck voltage and current, but don't subscribe to the automatic " set it to 40ma" kind of thing. So, I go by ear and check to make sure current and voltage are within specs. Same as everybody else, I suppose.

I like simple user orientated equipment. I'm more of a player than an electronics type. I don't like master volumes on amps, or pedals where every resistor is replaced with a pot, or every cap is replaced with a rotary switch. I couldn't care less how technically impressive a ckt is or isn't, as long as it sounds good. I think something that's occasionally forgotten here is that sometimes a pedal's/amps limitations, or perceived limitations, are what inspire you to work good tones out of them. Too much flexibility, mods, or whatever leads to sameness in sound. Some of the greatest sounds we know are unique, born of definate character of both the player and the equipment. I'm sure you've noticed some of the most popular OD builds here seem to get modded so that they are all voiced the same.

I think it's great that's in today's market you've designed a player orientated amp. If a player buys this amp, gets great tone, and can change tubes and rebias with no more effort than it takes to reheat pizza in a microwave, you've suceeded. And if even more players do the same, and none of them are even aware of what sets this amp apart from others, and all your hard R & D work, it means you've succeeded even more. Because none of them are having the technical aspects explained to them by techs when they get the repair bill.  

[Peter Snowberg]

Congratulations R.G.!!!

This is probably the single biggest thing I missed while on sabbatical.